One conventional example of a proximity sensor for detecting approach of an object based on capacitance is disclosed in Japanese Unexamined Patent Application Publication No. 2001-35327 A (Patent Document 1). The proximity sensor comprises a bottomed tubular fixed shield electrode 2, a disk-like detection substrate 7 provided at an opening end of the fixed shield electrode 2, a detection electrode 1 mounted on a central portion of the detection substrate 7 to face an object 11 to be detected, and a movable shield electrode 5 mounted outwardly of the fixed shield electrode 2 to be slidable along an axial direction of the tubular electrodes. In this proximity sensor, the movable shield electrode 5 is slid to adjust amount of projection from the fixed shield electrode 2 toward the object 11 to be detected thereby maintaining the detection electrode 1 and the movable shield electrode 5 in substantially the same potential. (The reference numbers used in this section are cited from Patent Document 1.)
With the above proximity sensor, a shielded portion that is covered by the shield electrode 5 and formed in a predetermined range of a side of the detection electrode 1 to extend from the detection electrode 1 toward the object to be detected is variable. Thus, it becomes possible to adjust an area, by the shield electrode 5, where an electric flux line formed between the detection electrode 1 and the object to be detected might undergo some influences.
The capacitance-type proximity sensor does not serve to exactly measure the distance to the object. On the other hand, the capacitance-type proximity sensor is superior in decay durability, dust tightness and simplicity in structure, dispensing with any electrical contact and further dispensing with mated light source and light-sensitive element as required in an optical proximity sensor using infrared rays, for example. Thus, the capacitance-type proximity sensor is effective for use in recognizing the presence of the object.
In the capacitance-type proximity sensor, the approach of the object is detected by variations of capacitance when the object approaches the electrode. Thus, it is difficult in the capacitance-type proximity sensor to accurately determine a detecting area relating to directional characteristics only with change of the configuration of the electrode. As a result, the capacitance-type proximity sensor may additionally require a shield exerting the influences on the electrode as described in Patent Document 1.
However, the provision of the shield easily contributes to increase of the size of the proximity sensor and thus leaves room for improvement. In particular, the proximity sensor capable of recognizing the object approaching from different directions is desired while such a sensor might be complicated as long as the shield is required.
Here, taking a rotary-type knob equipped with an electric device into consideration, it is also desired to provide a device using a proximity sensor capable of distinguishing between the case where the user rotates the knob properly and the case where the knob is unintentionally rotated when a sleeve of the user's clothing or part of the user's body contacts the knob.